This application claims the benefit of priority from Japanese Patent Applications Nos. 2001-079980, filed on Mar. 21, 2001, and 2001-316760, filed on Oct. 15, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electrophoresis display device using a dispersion liquid which comprises a plurality of electrophoresis particles dispersed in an insulating liquid.
2. Discussion of the Background
There is an expectation for a reflective display device for its low power consumption and to not be a burden on the eyes of a viewer. For example, an electrophoresis display device as described in U.S. Pat. No. 3,668,106 is a known reflective display device.
The electrophoresis display device includes a dispersion liquid or fluid and a pair of electrodes opposed to each other by interposing the dispersion liquid. The dispersion liquid includes an insulating liquid and electrophoresis particles possessing an electric charge dispersed in the insulating liquid. The electrophoresis particles are moved onto one of the pair of electrodes having an electric polarity opposite that of the electrophoresis particles by an applied electric field to the dispersion liquid via the electrodes, whereby a successive image is displayed. A background color which is contrastive to the electrophoresis particle is carried by the insulating liquid including pigment particles.
When the electrophoresis particles are adhered to a surface of the electrode near to an observational surface, the electrophoresis display device displays the color of the electrophoresis particles. Further, when the electrophoresis particles are adhered to a surface of an electrode remote from the observational surface, the color carried by the electrophoresis particles is concealed by the insulating liquid and the electrophoresis display device displays the color of the insulating liquid.
The electrophoresis display device has several advantages, such as a wide viewing angle, a high contrast and a low power consumption as described in, for example, Proc. SID. 18, 267 (1977). On the other hand, a simple matrix drive cannot be performed because it is difficult to provide a threshold characteristic between an applied voltage and display color property. Therefore, the electrode for each pixel needs to be provided with a switching element. However, the required applied voltage to the electrode is high, and therefore the thin film transistor technology used in a liquid crystal display is difficult to apply to the display device. Thus, a circuit of a switching element for the respective electrodes has to be formed on a board separate from the display panel. Further, the display panel and the board need to be connected by a plurality of wirings. Therefore, the larger the number of pixels, the larger the number of wirings and the device cannot be realized.
With regard to the structural problem of the electrophoresis display device, there are also examples enabling the simple matrix drive by employing devised structures, as described in Proc. SID. 18, 255 (1977) or SID 00 DIGEST, 24 (2000),
Another electrophoresis display device capable of performing the simple matrix drive is also described in Japanese Patent Laid-Open No. 2001-201770. This electrophoresis display device includes a structure holding an insulating liquid dispersed with electrophoresis particles between a first board having three types of electrodes and a second board having one type of electrode.
To attain a high resolution electrophoresis display device, a simple matrix structure is appreciated. However, according to the conventional technology, the simple matrix drive increases the cost of the display device because of its complicated structure.
The complicated cell structure, such as the device described in Proc. SID, 18, 255 (1977) or SID 00 DIGEST, 24 (2000), increases a cost of the display device and hampers high resolution formation. The device also includes a partition wall for providing a control electrode in the cell, and when the pixel size of display device for high resolution is downsized, there is a limit in thin film formation for the partition wall. Thus, a deterioration in the display characteristic is estimated because of the smaller aperture rate of each pixel.
An object of the present invention is to provide an electrophoresis display device which can attain a simple matrix drive with a simple structure.
To achieve these and other objects, the present invention provides an electrophoresis display device including a first board having a first surface, first electrodes disposed on the first surface, second electrodes disposed on the first surface in parallel with the first electrodes. Also included is a second board having a second surface facing the first surface, and third electrodes disposed on the second surface. Further, each of the third electrodes intersects with the first and second electrodes. The device further includes a dispersion liquid disposed between the first and the second boards and including an insulating liquid and a plurality of electrophoresis particles charged to a same electrical polarity. A first electrical potential supplying unit is also coupled to the first electrode and applies to the first electrode an initial voltage, a first hold voltage, and a rewriting voltage having a voltage value between the initial voltage and the first hold voltage. The first electrical potential supplying unit applies the intital, first hold and rewriting voltages in an order of the initial voltage, the rewriting voltage and the first hold voltage. Also included is a second electrical potential supplying unit coupled to the second electrode and configured to apply to the second electrode an intermediary voltage having a voltage value between the initial voltage and the rewriting voltage, and a third electrical potential supplying unit coupled to the third electrode and configured to apply to the third electrode a color display voltage or an image signal voltage having a voltage value different from the intermediary voltage, and a second hold voltage having a voltage value between the initial voltage and the rewriting voltage in synchronism with the first hold voltage.